High-performance PET / PC composite foam material based on supercritical CO2 extrusion foaming and preparation method thereof

Abstract

The invention provides a high-performance PET / PC (polyethylene terephthalate / polycarbonate) composite foam material based on supercritical CO2 extrusion foaming and a preparation method thereof, and the preparation method comprises the following steps: mixing polyethylene glycol terephthalate, polycarbonate and a chain extender to obtain a mixture; then the mixture is added into a supercritical fluid extrusion foaming device composed of two extruders connected in series, a gas injection port is formed in a cylinder of the first extruder, the first extruder achieves continuous gas injection, stable injection of the CO2 foaming agent is guaranteed, reverse escape of the CO2 foaming agent is prevented, and the second extruder achieves uniform mixing of the materials; and extruding and foaming through a capillary tube opening mold of a second extruder to obtain the high-performance PET / PC composite foam material. The high-performance PET / PC composite foam material is successfully prepared by taking supercritical CO2 as a foaming agent and adopting a self-developed extrusion foaming device, and meanwhile, continuous production of the material is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer material foaming, and relates to a high-performance PET / PC composite foam material based on supercritical CO2 extrusion foaming and a preparation method thereof, and in particular to the preparation using an extrusion foaming device disclosed in Chinese authorized invention patent CN109760333B. Background Art

[0002] With the advancement of industrialization, the requirements for material performance are constantly increasing. Traditional plastic materials may not meet the needs of specific industrial applications in some aspects. For example, the low mechanical strength of polyethylene (PE)[1] makes it impossible to be used in industry. However, some special industrial applications, such as ships, plywood core materials, aerospace, electronic equipment and other fields, have put forward higher requirements on the performance of materials. Therefore, people began to seek materials with better performance. Engineering plastics came into being and became one of the important materials to meet special industrial and technological needs. Engineering plastics are a type of high-performance plastic materials with excellent mechanical properties, chemical corrosion resistance, high temperature resistance and good insulation properties. These plastics are usually used in engineering applications that require high strength, high wear resistance, high temperature stability and chemical stability.

[0003] Polyethylene terephthalate (PET), commonly known as polyester, is one of the five major engineering plastics. It is successfully synthesized by esterification of terephthalic acid (DMT) and ethylene glycol (EG). Its molecular structure has a rigid benzene ring structure and a macromolecular chain of ester groups. These structural characteristics give it high strength performance. PET has a wide range of applications in industry. One of the most common uses is the manufacture of fibers, engineering products, and films. One of the most common applications of PET fiber is the manufacture of clothing, bedding, and other textiles. PET also has good physical properties, such as friction resistance, fatigue resistance, and chemical corrosion resistance.

[0004] Due to the high crystallinity and high melting point of PET materials, the PET foam obtained after foaming has high thermal stability and excellent mechanical strength. Due to the above advantages, PET foam has been widely used in structural core materials, such as the inner core of wind turbine blades and composite sandwich panels. In addition, lightweight and high-strength PET foam is also widely used in rail transportation, ships, building walls and other fields. PET foam also has excellent wear resistance, flame retardancy and heat insulation properties, which gives it unique advantages in food packaging and other fields.

[0005] Conventional PET has a low molecular weight and a narrow molecular weight distribution, resulting in low melt strength[1]. Due to the low melt strength, the cells in the melt are easily broken after severe tensile deformation, resulting in uneven cell structure and low foaming ratio, which makes the mechanical properties of PET foam plastics too low[2]. In addition, PET has strong water absorption and is very easy to decompose at the melt processing temperature (250-290℃) after absorbing water. Since the processing temperature is close to its decomposition temperature (300℃), its foaming temperature window is narrow, which limits its application in the foaming field[3]. At the same time, since PET crystals restrict the movement of chain segments, the solubility of CO2 in PET is low, and the number of bubble nuclei formed during the foaming process is insufficient, which also limits its application and preparation in supercritical CO2 foaming technology[4].

[0006] In view of the above-mentioned shortcomings of PET, many researchers have adopted methods such as in-situ copolymerization, blending modification, and reactive extrusion modification to improve the foaming properties of PET[5]. Xanthos et al.[6] improved the viscoelasticity of R-PET by solid phase polycondensation. The density of the prepared modified PET after extrusion foaming can reach as low as 0.2 g / cm 3 The pore size can reach 270μm. Xia et al. [7] compounded nanoclay, PMDA and PET, and then used supercritical CO2 as a foaming agent to prepare a foam with a pore size of 29-53μm and a pore density of 6.5×107-6.9×10 8 cells / cm 3 , PET composite foam with a foaming ratio of more than 10 times. Yan[8] et al. used chain extender (PMDA) and 1,3,5-triglyceride isocyanurate (TGIC) as modifiers, combined reaction extrusion and solid phase polycondensation methods, and prepared highly viscoelastic modified PET. Bocz[9] et al. used ADR (an epoxy multifunctional oligomer) as a modifier to modify recycled PET, and further increased the molecular weight of PET by solid phase polycondensation. Jiang

[10] et al. introduced PTFE (polytetrafluoroethylene) fiber into the PET matrix by melt composite method, and foamed the modified PET by intermittent foaming method using CO2 as a foaming agent.

[0007] However, in the above-mentioned prior art, the intermittent foaming process used is usually a non-continuous process, which is not conducive to actual industrial conversion production. At the same time, the modification / chain extension / copolymerization of PET must involve multiple process steps, and the overall process method is too complicated. In addition, the chemical modifiers, foaming agents and chain extenders usually involved are often accompanied by risks such as toxicity and easy residues. In the actual production process, the use and addition of such additives should be reduced as much as possible.

[0008] Therefore, there is an urgent need for a method with simple process and continuous production to obtain a PET foam material with high foaming ratio, high strength and excellent pore structure, which will have a very broad application prospect. Summary of the invention

[0009] The purpose of the present invention is to solve the problems in the above-mentioned background technology, and to provide a high-performance PET / PC composite foam material based on supercritical CO2 extrusion foaming and a preparation method thereof. Supercritical CO2 is used as a foaming agent, and an independently developed extrusion foaming device is adopted to successfully prepare a high-performance PET / PC composite foam material with an excellent pore structure. At the same time, continuous production of the material is realized, which lays a solid theoretical and experimental foundation for the preparation of PET / PC extrusion foam products.

[0010] To achieve the above objectives, the present invention is implemented by adopting a technical solution consisting of the following technical measures.

[0011] A method for preparing a high-performance PET / PC composite foam material based on supercritical CO2 extrusion foaming mainly comprises the following steps:

[0012] (1) The following main raw material components are mixed by weight to form a mixed material:

[0013] Polyethylene terephthalate (PET) 84.4-98.4 parts,

[0014] Polycarbonate (PC) 1-15 parts,

[0015] Chain extender 0.6 parts,

[0016] The total weight of polyethylene terephthalate, polycarbonate and chain extender is 100 parts;

[0017] (2) adding the mixed material obtained in step (1) into a supercritical fluid extrusion foaming device composed of two extruders connected in series, wherein a gas injection port is provided on the barrel of the first extruder, and the first extruder realizes continuous gas injection to ensure the smooth injection of CO2 foaming agent and prevent the CO2 foaming agent from escaping in the reverse direction, and the second extruder realizes uniform mixing of the materials, and extrusion foaming is performed through the capillary die of the second extruder to obtain a high-performance PET / PC composite foam material.

[0018] In this article, the polyethylene terephthalate (PET) described in step (1) is a conventional PET raw material selected in the field of chemical materials. Those skilled in the art can select a suitable PET variety according to specific needs and process requirements, or can refer to the conventional PET selection in the application field of the final product.

[0019] In this article, the polycarbonate (PC) described in step (1) is a conventional PC raw material selected in the field of chemical materials. Those skilled in the art can select a suitable PC variety according to specific needs and process requirements, or can refer to conventional PC selection in the application field of the final product.

[0020] In this article, due to the low melt strength of the polyethylene terephthalate (PET), pure PET is generally considered difficult to be molded into a foam material during the extrusion foaming process, and it is often necessary to modify it. However, the chemical modifiers and chain extenders usually involved are often accompanied by risks such as toxicity and easy residue. The use and addition of such additives should be reduced as much as possible in the actual production process; in addition, the modification process usually requires additional process steps. In the present invention, due to the use of the patented equipment (CN109760333B) owned by the applicant, a supercritical fluid extrusion foaming device composed of two series-connected extruders is used to achieve continuous modification and extrusion foaming, which greatly simplifies the process method on the one hand; on the other hand, based on the application of the patented equipment, through comparative test exploration, it is surprisingly found that only a very small amount (0.6wt%) of chain extender is added to achieve the modification of PET during the extrusion process. Compared with the technical solutions related to PET modification in the prior art, the use of chain extenders is significantly reduced, making the technical solution of the present invention healthier and more environmentally friendly as a whole.

[0021] In this article, the chain extender in step (1) is a conventional chain extender in the chemical industry that can be used for chain extension modification of polyethylene terephthalate (PET), such as polyepoxy chain extender (ADR-4300F), pentaerythritol, pyromellitic anhydride (PMDA), glycerol triol, triglycidyl isocyanurate (TGIC), glycidyl methacrylate (GMA), trimethylolpropane triacrylate (TMPTA), hexamethylene-1,6-diisocyanate (HDI), 2,5-dimethyl -2,5-di(tert-butylperoxy)hexane (T101), epoxidized cardanol (Ecard), thermoplastic polyurethane elastomer (TPU), 4,4'-methylene diisocyanate (MDI), polyepoxy chain extender (ADR-4468), 4,4'-diaminodiphenylmethane tetraglycidyl epoxy resin (TGDDM), tetrahydrophthalic acid diglycidyl ester (TADE), 4-vinylbenzyl glycidyl ether (VBGE) or at least one of cyclic peroxide (T301).

[0022] In one of the technical solutions, it is found through comparative experiments that the chain extender in step (1) is preferably pyromellitic anhydride (PMDA).

[0023] In this article, the supercritical fluid extrusion foaming device composed of two series-connected extruders in step (2) is the extrusion foaming device disclosed in the previously authorized patent CN109760333B of the applicant of the present invention. In step (2), the first extruder realizes continuous gas injection, and the second extruder realizes uniform mixing of materials, which can be referred to the same description in the previously authorized patents CN109760333B and CN109762200B of the present invention application, especially the preparation method and description similar to the present invention are adopted in the previously authorized patent CN109762200B. In order to facilitate those skilled in the art to understand the preparation method of the present invention, the following technical content can also be referred to:

[0024] Specifically, the continuous gas injection is realized by the following structure: comprising a gas injection port (1) arranged on a first extruder and a gas injection section (2) arranged on a screw; the gas injection port (1) and the gas injection section (2) are matched with each other; a plurality of screw ridges (3) are arranged at intervals in the circumferential direction of the screw in the gas injection section (2); and a material trough (4) is formed between two adjacent screw ridges (3) along the circumference of the screw.

[0025] Specifically, the uniform mixing is achieved by the following structure: the screw (21) of the second extruder includes a dispersion mixing section (36), and non-equidistantly segmented dispersion thread sections (24) are sequentially arranged along the axial direction on the screw (21) of the dispersion mixing section (36); the thread (25) located in the latter dispersion thread section (24) between two adjacent dispersion thread sections (24) starts between the two threads (25) in the former dispersion thread section (24).

[0026] The main inventive point of the present invention is that there is no report on PET / PC supercritical CO2 foaming material, so its foaming behavior and mechanism through supercritical carbon dioxide are still unclear. Based on this, the inventor of the present invention studied the foaming behavior and mechanism of PET / PC blending system. The inventor blended a relatively small amount of PC and PET, and deeply studied the material properties and foaming performance of PET / PC, the interaction between PET and PET / PC system and CO2, and found that CO2 can not only be used as a foaming agent, but also as a plasticizer to promote the transformation of PET's crystal structure to an amorphous structure, and ultimately improve the quality of the foam. Using the self-developed supercritical fluid extrusion foaming device, by selecting a capillary die, PET / PC foam material was successfully prepared, and its continuous production was realized, and the influence of PC content and process parameters such as die temperature, CO2 injection amount and screw speed on PET / PC supercritical carbon dioxide extrusion foaming behavior was deeply explored. These studies provide empirical evidence for the efficient and continuous production of PET-based foams, which are of great value and significance in theory and practical operation.

[0027] In addition, the supercritical fluid extrusion foaming device composed of two extruders connected in series used in the present invention also has an important influence on the supercritical CO2 extrusion foaming behavior. The device is composed of two single-screw extruders connected in series, and the die of the second extruder head is a capillary die. The pressure drop △P of the head has an important influence on the pore structure. When other conditions are constant, the larger the pressure drop △P, the more obvious the downward trend of free energy during the formation of bubble nuclei in the system, which makes the nucleation process easier, thereby promoting the formation of excellent pore structure. For PET, the melt strength can be improved after the matrix and chain extender and PC are blended. When the homogeneous system of polymer melt / CO2 flows out from the capillary die of the head, a huge pressure difference will be formed, which will induce gas nucleation, thereby preparing foam filaments with excellent pore structure. Under the condition of certain process parameters, △P is inversely proportional to the head coefficient K. The formula of the head coefficient K of the circular head is:

[0028]

[0029] Where K is the head coefficient (cm 3 ), R is the hole diameter (cm), L is the shaping length (cm). It can be seen from the formula that K is proportional to the fourth power of R and inversely proportional to the first power of L. R has a greater influence on K, so the smaller the hole diameter of the die, the smaller the die coefficient of the die, and thus the larger △P. A larger △P is conducive to forming a good foaming effect and preparing a foam with an excellent pore structure. The present invention adopts a capillary die, which is more suitable for extrusion foaming of PET. Instructions attached Fig.10 The process of preparing high-performance PET / PC composite foam materials using a capillary die is demonstrated. Fig.10 It can also be seen that when the melt flows out of the capillary die of the die head, it starts to foam immediately, and the extrusion process is very stable.

[0030] In one of the technical solutions, in order to better achieve uniform extrusion foaming of the bubbles, the temperature of the first extruder is 240-280°C, and the temperature of the second extruder is 250-280°C.

[0031] In one of the technical solutions, in order to better achieve uniform extrusion foaming of the cells, the screw speed of the first extruder is 20 to 100 r / min, and the screw speed of the second extruder is 5 to 20 r / min.

[0032] In one of the more preferred technical solutions, it was found through comparative experiments that in order to comprehensively achieve a better expansion ratio and pore size, the polycarbonate in step (1) is 4 to 6 parts.

[0033] It should be noted that, from the comparative experiment, when the polycarbonate content is 1wt%, the expansion ratio of the PET / PC composite foam is also significantly lower, the foam cell size is small and the cell wall is thick, the foam is difficult to form during the extrusion process, and the cell collapse occurs. As the polycarbonate content increases to 5wt%, the foam expansion ratio reaches the highest and the cell size becomes larger. However, as the polycarbonate content further increases, not only the cell size of the foam decreases, but also the expansion ratio decreases.

[0034] The above findings are obviously different from the conventional knowledge about PET / PC blending system in the prior art. For example, Ren et al.

[11] found that when the weight ratio of PET / PC was 50 / 50, the tensile strength of PET / PC micro-pieces was 15.5% higher than that of PET micro-pieces. Therefore, it is shown that the ratio of PET / PC blending system in the prior art cannot be applied to the supercritical CO2 extrusion foaming PET / PC composite foam material system.

[0035] In one of the more preferred technical solutions, it was found through comparative experiments that in order to comprehensively achieve a better foaming ratio and pore size, the diameter of the circular hole of the capillary die in step (2) is 2 mm, and the temperature of the capillary die is 260-266°C.

[0036] It should be noted that from the comparative experiment, when the die temperature is low (254°C), the cell size of the foam is large and the cell density is small; when the die temperature rises to 260°C, the cell size of the foam decreases and the cell density increases. This shows that increasing the temperature can promote the uniformity and densification of the foam cell distribution. When the temperature is further increased to 266°C, the cell size reaches the maximum, and the foaming ratio also reaches the highest at this time. It can also be found that when the die temperature is 254°C, the cell wall thickness of the PET / PC composite foam is very thick; when the temperature rises to 266°C, it can be observed that the cell wall of the foam is broken and the cell wall is also very thin, indicating that it is the upper limit temperature of the foam foaming. Therefore, it is not advisable to increase the temperature of the die excessively. The above comparative experimental results show that PET / PC is more sensitive to temperature during extrusion foaming, so the temperature of the die needs to be more accurately controlled during foaming.

[0037] In one of the more preferred technical solutions, it is found through comparative experiments that in order to achieve a better foaming ratio and cell size, the continuous gas injection in step (2) has a gas injection rate of 3.8 to 7.2 ml / min. Usually, a conventional supercritical fluid gas injection system is used for gas injection.

[0038] It should be noted that from the comparative experiment, when the CO2 foaming agent injection amount is 1ml / min, the foaming effect is not good, and the foam has a large cell size and a small foaming ratio; when the CO2 foaming agent is 4ml / min, the strong plasticizing effect causes the crystalline area of ​​the PET matrix to transform into an amorphous area, which is more conducive to the nucleation of CO2, so that the nucleation sites increase and improve, thereby forming a dense cell structure. When the CO2 foaming agent injection amount is further increased to 7ml / min, the growth of the pores is promoted and the foaming ratio reaches the best. However, when the CO2 foaming agent injection amount is increased to 10ml / min, the prepared foam begins to shrink, so it is not advisable to continue to increase the CO2 foaming agent injection amount. The exploration results of different CO2 foaming agent injection amounts show that it is necessary to control the appropriate injection amount during the foaming process, because too low an injection amount will make the foam expansion ratio too low, and too high an injection amount will cause the foam surface to shrink, which is not conducive to the preparation of foams with good performance.

[0039] In one of the more preferred technical solutions, it was found through comparative experiments that in order to comprehensively achieve a better foaming ratio and pore size, the screw speed of the second extruder in step (2) is 5 to 10 r / min.

[0040] It should be noted that, from the comparative experiment, when the screw speed is less than 10r / min, the cell size and expansion ratio of the foam gradually increase with the increase of the screw speed, while the cell density gradually decreases. However, when the screw speed is further increased to 15r / min, the excessively high speed leads to a sudden drop in the strength of the system. At this time, the prepared foam has a shrinkage phenomenon of the surface on the macro level, and the shrinkage of the cells on the micro level, and the expansion ratio also decreases significantly.

[0041] The present invention has the following beneficial effects:

[0042] (1) The present invention provides a high-performance PET / PC composite foam material based on supercritical CO2 extrusion foaming and a preparation method thereof. By blending polycarbonate (PC) with high melt strength and amorphous structure with polyethylene terephthalate (PET) with low melt strength and high crystallinity, the melt strength of the PET matrix is ​​improved, the crystallinity of the PET matrix is ​​reduced, and the solubility of the CO2 foaming agent is improved, which is beneficial to the subsequent supercritical CO2 foaming process.

[0043] (2) The present invention uses supercritical CO2 as a foaming agent and an independently developed extrusion foaming device to successfully prepare a high-performance PET / PC composite foam material with an excellent pore structure, while realizing continuous production of the material, laying a solid theoretical and experimental foundation for the preparation of PET / PC extrusion foam products.

[0044] (3) In one of the technical solutions, the effects of different polycarbonate (PC) contents and different process parameters (die temperature, CO2 injection volume, screw speed, etc.) on the pore parameters (pore size, pore density) and foaming ratio of PET / PC foam strips were systematically analyzed, which opened up a new path for the continuous production of PET-based foams and provided practical experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a schematic diagram of the extrusion foaming device used in the present invention.

[0046] Figure 2 This is a schematic diagram of the structure of the barrel and screw in the first extruder.

[0047] Figure 3 for Figure 2 Cross-sectional view of section AA.

[0048] Figure 4 This is a schematic diagram of the structure of the first extruder screw.

[0049] Figure 5 for Figure 4 A magnified schematic diagram of local area I.

[0050] Figure 6 for Figure 5 Cross-sectional view of section CC.

[0051] Figure 7 Schematic diagram of the structure of the screw of the second extruder.

[0052] Figure 8 for Figure 7 A magnified schematic diagram of the local area Q in the figure.

[0053] Fig. 9 This is a real photo of the extrusion foaming device used in the present invention.

[0054] Fig.10 The following are photos of the extrusion process of preparing high-performance PET / PC composite foam material using a capillary die according to the present invention, wherein (a) is a front view photo and (b) is a side view photo.

[0055] Fig.11 The SEM images of the cross-sections of the PET / PC foam strips prepared in Examples 1 to 4 of the present invention and the corresponding pore size distribution diagrams are shown. Among them, (a) and (e) correspond to the PET / PC foam strips prepared in Example 1; (b) and (f) correspond to the PET / PC foam strips prepared in Example 2; (c) and (g) correspond to the PET / PC foam strips prepared in Example 3; (d) and (h) correspond to the PET / PC foam strips prepared in Example 4.

[0056] Fig.12 The figure is a comparative line graph of the cell size (a), cell density (b) and expansion ratio (c) of the PET / PC foam strips prepared in Examples 1 to 4 of the present invention.

[0057] Fig.13 The SEM images and corresponding pore size distribution diagrams of the cross-sections of the PET / PC foam strips prepared in Examples 5 to 6 and Comparative Example 1 of the present invention. Among them, (a) and (d) correspond to the PET / PC foam strips prepared in Comparative Example 1; (b) and (e) correspond to the PET / PC foam strips prepared in Example 5; (c) and (f) correspond to the PET / PC foam strips prepared in Example 6.

[0058] Fig.14 It is a comparative line graph of the cell size (a), cell density (b) and expansion ratio (c) of the PET / PC foam strips prepared in Examples 5 to 6 of the present invention and Comparative Example 1.

[0059] Fig.15 The SEM images and corresponding pore size distribution diagrams of the cross-sections of the PET / PC foam strips prepared in Examples 7 to 8 of the present invention and Comparative Example 2 are shown. Among them, (a) and (d) correspond to the PET / PC foam strips prepared in Comparative Example 2; (b) and (e) correspond to the PET / PC foam strips prepared in Example 7; (c) and (f) correspond to the PET / PC foam strips prepared in Example 8.

[0060] Fig.16 It is a comparative line graph of the cell size (a), cell density (b) and expansion ratio (c) of the PET / PC foam strips prepared in Examples 7 to 8 of the present invention and Comparative Example 2.

[0061] Fig.17 The SEM images and corresponding pore size distribution diagrams of the cross-sections of the PET / PC foam strips prepared in Examples 9 to 11 and Comparative Example 3 of the present invention are shown. Among them, (a) and (e) correspond to the PET / PC foam strips prepared in Comparative Example 3; (b) and (f) correspond to the PET / PC foam strips prepared in Example 9; (c) and (g) correspond to the PET / PC foam strips prepared in Example 10; (d) and (h) correspond to the PET / PC foam strips prepared in Example 11.

[0062] Fig.18 It is a comparative line graph of the cell size (a), cell density (b) and expansion ratio (c) of the PET / PC foam strips prepared in Examples 9 to 11 of the present invention and Comparative Example 3.

[0063] Marked in the figure are: gas injection port 1, gas injection section 2, screw rib 3, material trough 4, feeding section 5, shielding conveying section 6, screw rib mixing section 7, first extruder 8, gas injection equipment 9, first barrel 10, first screw 12, first feed port 13, first extrusion port 14, gas injection pipeline 15, second extruder 18, second screw 21, dispersed thread section 24, thread 25, foaming die 26, screw rib mixing section 35, dispersed mixing section 36. DETAILED DESCRIPTION

[0064] In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve it. It is particularly important to point out that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously change or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention. Although it is believed that those of ordinary skill in the art fully understand the following terms, the following definitions are still stated to help illustrate the subject matter disclosed by the present invention.

[0065] A method for preparing a high-performance PET / PC composite foam material based on supercritical CO2 extrusion foaming mainly comprises the following steps:

[0066] (1) The following main raw material components are mixed by weight to form a mixed material:

[0067] Polyethylene terephthalate (PET) 84.4-98.4 parts,

[0068] Polycarbonate (PC) 1-15 parts,

[0069] Chain extender 0.6 parts,

[0070] The total weight of polyethylene terephthalate, polycarbonate and chain extender is 100 parts;

[0071] (2) adding the mixed material obtained in step (1) into a supercritical fluid extrusion foaming device composed of two extruders connected in series, wherein a gas injection port is provided on the barrel of the first extruder, and the first extruder realizes continuous gas injection to ensure the smooth injection of CO2 foaming agent and prevent the CO2 foaming agent from escaping in the reverse direction, and the second extruder realizes uniform mixing of the materials, and extrusion foaming is performed through the capillary die of the second extruder to obtain a high-performance PET / PC composite foam material.

[0072] In this article, the polyethylene terephthalate (PET) described in step (1) is a conventional PET raw material selected in the field of chemical materials. Those skilled in the art can select a suitable PET variety according to specific needs and process requirements, or can refer to the conventional PET selection in the application field of the final product.

[0073] In this article, the polycarbonate (PC) described in step (1) is a conventional PC raw material selected in the field of chemical materials. Those skilled in the art can select a suitable PC variety according to specific needs and process requirements, or can refer to conventional PC selection in the application field of the final product.

[0074] In this article, due to the low melt strength of the polyethylene terephthalate (PET), pure PET is generally considered difficult to be molded into a foam material during the extrusion foaming process, and it is often necessary to modify it. However, the chemical modifiers and chain extenders usually involved are often accompanied by risks such as toxicity and easy residue. The use and addition of such additives should be reduced as much as possible in the actual production process; in addition, the modification process usually requires additional process steps. In the present invention, due to the use of the patented equipment (CN109760333B) owned by the applicant, a supercritical fluid extrusion foaming device composed of two series-connected extruders is used to achieve continuous modification and extrusion foaming, which greatly simplifies the process method on the one hand; on the other hand, based on the application of the patented equipment, through comparative test exploration, it is surprisingly found that only a very small amount (0.6wt%) of chain extender is added to achieve the modification of PET during the extrusion process. Compared with the technical solutions related to PET modification in the prior art, the use of chain extenders is significantly reduced, making the technical solution of the present invention healthier and more environmentally friendly as a whole.

[0075] In this article, the chain extender in step (1) is a conventional chain extender in the chemical industry that can be used for chain extension modification of polyethylene terephthalate (PET). In one embodiment, for example, polyepoxy chain extender (ADR-4300F), pentaerythritol, pyromellitic anhydride (PMDA), glycerol triol, triglycidyl isocyanurate (TGIC), glycidyl methacrylate (GMA), trimethylolpropane triacrylate (TMPTA), hexamethylene-1,6-diisocyanate (HDI), 2, At least one of 5-dimethyl-2,5-di(tert-butylperoxy)hexane (T101), epoxidized cardanol (Ecard), thermoplastic polyurethane elastomer (TPU), 4,4'-methylene diisocyanate (MDI), polyepoxy chain extender (ADR-4468), 4,4'-diaminodiphenylmethane tetraglycidyl epoxy resin (TGDDM), tetrahydrophthalic acid diglycidyl ester (TADE), 4-vinylbenzyl glycidyl ether (VBGE) or cyclic peroxide (T301).

[0076] In one embodiment, it is found through comparative experiments that the chain extender in step (1) is preferably pyromellitic anhydride (PMDA).

[0077] In this article, the supercritical fluid extrusion foaming device composed of two series-connected extruders in step (2) is the extrusion foaming device disclosed in the previously authorized patent CN109760333B of the applicant of the present invention. In step (2), the first extruder realizes continuous gas injection, and the second extruder realizes uniform mixing of materials, which can be referred to the same description in the previously authorized patents CN109760333B and CN109762200B of the present invention application, especially the preparation method and description similar to the present invention are adopted in the previously authorized patent CN109762200B. In order to facilitate those skilled in the art to understand the preparation method of the present invention, the following technical content can also be referred to:

[0078] Specifically, the continuous gas injection is realized by the following structure: comprising a gas injection port (1) arranged on a first extruder and a gas injection section (2) arranged on a screw; the gas injection port (1) and the gas injection section (2) are matched with each other; a plurality of screw ridges (3) are arranged at intervals in the circumferential direction of the screw in the gas injection section (2); and a material trough (4) is formed between two adjacent screw ridges (3) along the circumference of the screw.

[0079] Specifically, the uniform mixing is achieved by the following structure: the screw (21) of the second extruder includes a dispersion mixing section (36), and non-equidistantly segmented dispersion thread sections (24) are sequentially arranged along the axial direction on the screw (21) of the dispersion mixing section (36); the thread (25) located in the latter dispersion thread section (24) between two adjacent dispersion thread sections (24) starts between the two threads (25) in the former dispersion thread section (24).

[0080] The main inventive point of the present invention is that there is no report on PET / PC supercritical CO2 foaming material, so its foaming behavior and mechanism through supercritical carbon dioxide are still unclear. Based on this, the inventor of the present invention studied the foaming behavior and mechanism of PET / PC blending system. The inventor blended a relatively small amount of PC and PET, and deeply studied the material properties and foaming performance of PET / PC, the interaction between PET and PET / PC system and CO2, and found that CO2 can not only be used as a foaming agent, but also as a plasticizer to promote the transformation of PET's crystal structure to an amorphous structure, and ultimately improve the quality of the foam. Using the self-developed supercritical fluid extrusion foaming device, by selecting a capillary die, PET / PC foam material was successfully prepared, and its continuous production was realized, and the influence of PC content and process parameters such as die temperature, CO2 injection amount and screw speed on PET / PC supercritical carbon dioxide extrusion foaming behavior was deeply explored. These studies provide empirical evidence for the efficient and continuous production of PET-based foams, which are of great value and significance in theory and practical operation.

[0081] In addition, the supercritical fluid extrusion foaming device composed of two extruders connected in series used in the present invention also has an important influence on the supercritical CO2 extrusion foaming behavior. The device is composed of two single-screw extruders connected in series, and the die of the second extruder head is a capillary die. The pressure drop △P of the head has an important influence on the pore structure. When other conditions are constant, the larger the pressure drop △P, the more obvious the downward trend of free energy during the formation of bubble nuclei in the system, which makes the nucleation process easier, thereby promoting the formation of excellent pore structure. For PET, the melt strength can be improved after the matrix and chain extender and PC are blended. When the homogeneous system of polymer melt / CO2 flows out from the capillary die of the head, a huge pressure difference will be formed, which will induce gas nucleation, thereby preparing foam filaments with excellent pore structure. Under the condition of certain process parameters, △P is inversely proportional to the head coefficient K. The formula of the head coefficient K of the circular head is:

[0082]

[0083] Where K is the head coefficient (cm 3 ), R is the hole diameter (cm), L is the shaping length (cm). It can be seen from the formula that K is proportional to the fourth power of R and inversely proportional to the first power of L. R has a greater influence on K, so the smaller the hole diameter of the die, the smaller the die coefficient of the die, and thus the larger △P. A larger △P is conducive to forming a good foaming effect and preparing a foam with an excellent pore structure. The present invention adopts a capillary die, which is more suitable for extrusion foaming of PET. Instructions attached Fig.10The process of preparing high-performance PET / PC composite foam materials using a capillary die is demonstrated. Fig.10 It can also be seen that when the melt flows out of the capillary die of the die head, it starts to foam immediately, and the extrusion process is very stable.

[0084] In one embodiment, in order to better achieve uniform extrusion foaming of the cells, the temperature of the first extruder is 240-280°C, and the temperature of the second extruder is 250-280°C.

[0085] In one embodiment, in order to better achieve uniform extrusion foaming of the cells, the screw speed of the first extruder is 20 to 100 r / min, and the screw speed of the second extruder is 5 to 20 r / min.

[0086] In one of the more preferred embodiments, it is found through comparative experiments that in order to comprehensively achieve a better expansion ratio and pore size, the polycarbonate in step (1) is 4 to 6 parts.

[0087] It should be noted that, from the comparative experiment, when the polycarbonate content is 1wt%, the expansion ratio of the PET / PC composite foam is also significantly lower, the foam cell size is small and the cell wall is thick, the foam is difficult to form during the extrusion process, and the cell collapse occurs. As the polycarbonate content increases to 5wt%, the foam expansion ratio reaches the highest and the cell size becomes larger. However, as the polycarbonate content further increases, not only the cell size of the foam decreases, but also the expansion ratio decreases.

[0088] The above findings are obviously different from the conventional knowledge about PET / PC blending system in the prior art. For example, Ren et al.

[11] found that when the weight ratio of PET / PC was 50 / 50, the tensile strength of PET / PC micro-pieces was 15.5% higher than that of PET micro-pieces. Therefore, it is shown that the ratio of PET / PC blending system in the prior art cannot be applied to the supercritical CO2 extrusion foaming PET / PC composite foam material system.

[0089] In one of the more preferred embodiments, it was found through comparative experiments that in order to comprehensively achieve a better foaming ratio and pore size, the diameter of the circular hole of the capillary die in step (2) is 2 mm, and the temperature of the capillary die is 260-266°C.

[0090] It should be noted that from the comparative experiment, when the die temperature is low (254°C), the cell size of the foam is large and the cell density is small; when the die temperature rises to 260°C, the cell size of the foam decreases and the cell density increases. This shows that increasing the temperature can promote the uniformity and densification of the foam cell distribution. When the temperature is further increased to 266°C, the cell size reaches the maximum, and the foaming ratio also reaches the highest at this time. It can also be found that when the die temperature is 254°C, the cell wall thickness of the PET / PC composite foam is very thick; when the temperature rises to 266°C, it can be observed that the cell wall of the foam is broken and the cell wall is also very thin, indicating that it is the upper limit temperature of the foam foaming. Therefore, it is not advisable to increase the temperature of the die excessively. The above comparative experimental results show that PET / PC is more sensitive to temperature during extrusion foaming, so the temperature of the die needs to be more accurately controlled during foaming.

[0091] In one of the more preferred embodiments, it is found through comparative experiments that in order to achieve a better foaming ratio and cell size, the continuous gas injection in step (2) has a gas injection rate of 3.8 to 7.2 ml / min. The gas injection is usually performed using a conventional supercritical fluid gas injection system.

[0092] It should be noted that from the comparative experiment, when the CO2 foaming agent injection amount is 1ml / min, the foaming effect is not good, and the foam has a large cell size and a small foaming ratio; when the CO2 foaming agent is 4ml / min, the strong plasticizing effect causes the crystalline area of ​​the PET matrix to transform into an amorphous area, which is more conducive to the nucleation of CO2, so that the nucleation sites increase and improve, thereby forming a dense cell structure. When the CO2 foaming agent injection amount is further increased to 7ml / min, the growth of the pores is promoted and the foaming ratio reaches the best. However, when the CO2 foaming agent injection amount is increased to 10ml / min, the prepared foam begins to shrink, so it is not advisable to continue to increase the CO2 foaming agent injection amount. The exploration results of different CO2 foaming agent injection amounts show that it is necessary to control the appropriate injection amount during the foaming process, because too low an injection amount will make the foam expansion ratio too low, and too high an injection amount will cause the foam surface to shrink, which is not conducive to the preparation of foams with good performance.

[0093] In one of the more preferred embodiments, it is found through comparative experiments that in order to comprehensively achieve a better expansion ratio and cell size, the screw speed of the second extruder in step (2) is 5 to 10 r / min.

[0094] It should be noted that, from the comparative experiment, when the screw speed is less than 10r / min, the cell size and expansion ratio of the foam gradually increase with the increase of the screw speed, while the cell density gradually decreases. However, when the screw speed is further increased to 15r / min, the excessively high speed leads to a sudden drop in the strength of the system. At this time, the prepared foam has a shrinkage phenomenon of the surface on the macro level, and the shrinkage of the cells on the micro level, and the expansion ratio also decreases significantly.

[0095] The screw in the extrusion foaming device of the present invention is a screw used in the foaming device; since the foaming device needs to inject a foaming agent, a corresponding gas injection port 1 structure needs to be provided on the foaming device, as shown in the attached Figure 3 As shown in the figure, the gas injection port 1 is arranged on the first barrel 10. The gas injection port 1 is used to inject a foaming agent into the extrusion channel so that the foaming agent and the material melt in the extrusion channel are fully mixed and then extruded to form a foamed product. The material melt is usually a thermoplastic polymer material; in addition, a corresponding nucleating agent, a plasticizer or other material components can be added as needed; and the foaming agent can usually be one or more of supercritical carbon dioxide, nitrogen, water, butane, and pentane, depending on the product requirements, and there is no strict restriction.

[0096] The screw of the present invention is provided with a feed end and a discharge end along the extrusion direction of the screw, and a gas injection section 2 corresponding to the gas injection port 1 on the extrusion foaming device is provided between the feed end and the discharge end; a plurality of screw ridges 3 are provided at intervals in the circumferential direction of the screw in the gas injection section 2; and a material passing groove 4 is formed between two adjacent screw ridges 3 along the circumference of the screw. For details, please refer to the attached Figure 4 To Attachment Figure 6 As shown in the figure, the gas injection section 2 of the screw rod of the present invention should correspond to the gas injection port 1 on the foaming device after installation, as shown in the attached figure. Figure 2 and attached Figure 3As shown in , when the screw is rotating, the gas injection port 1 will correspond to the screw rib 3 and the feed trough 4 at intervals, so that the gas injection port 1 can be intermittently connected with the feed trough 4; and the feed trough 4 is the channel through which the material melt passes, so when the corresponding feed trough 4 rotates to correspond to the gas injection port 1, the foaming agent can be injected into the material melt in the feed trough 4; and when the corresponding screw rib 3 rotates to correspond to the gas injection port 1, the gas injection port 1 can be temporarily blocked by the screw rib 3. In addition, in order to ensure a good blocking effect on the gas injection port 1, the size of the part on the screw rib 3 that matches the gas injection port 1 should not be less than the size of the mouth of the gas injection port 1; and according to the size relationship between the relative matching parts on the screw rib 3 and the gas injection port 1, the length of time for each screw rib 3 to block the gas injection port 1 can be determined in combination with the rotation speed of the screw. Temporary blocking of the gas injection port 1 by the screw rib 3 can play the following role: by blocking the gas injection port 1 at intervals, regular interval gas injection can be achieved, and the gas injection pressure of the gas injection port 1 can be made to fluctuate regularly, and the pressure of the gas injection port 1 during each gas injection can be increased, thereby alleviating the material melt from blocking the gas injection port 1, ensuring the gas injection effect and preventing the material melt from overflowing from the gas injection port in the opposite direction, thereby finally achieving stable and continuous gas injection of the gas injection pump.

[0097] In addition, without loss of generality, in order to ensure the effective rotation of the screw in the barrel of the extruder, there should theoretically be a certain gap between the screw and the barrel after assembly. Therefore, when the screw rib 3 rotates with the screw and corresponds to the gas injection port 1, there may theoretically be a certain gap. However, the sealing effect of the screw rib 3 on the gas injection port 1 can be ensured by setting the gap between the screw rib 3 and the gas injection port 1 to be close to zero.

[0098] More preferably, in the present invention, the screw ribs 3 arranged along the circumference of the screw can be arranged at even intervals, and the formed feed grooves 4 are also evenly distributed at intervals, so that when the screw is rotating at a uniform speed, the pressure fluctuation at the gas injection port 1 and the frequency of gas injection will show uniform changes, making the gas injection process more uniform and stable. And in theory, the present invention has no strict restrictions on the number of screw ribs 3 arranged along the circumference of the screw. In theory, at least one screw rib 3 can be arranged, and a corresponding feed groove 4 will be formed; or multiple screw ribs 3 can be arranged, and multiple feed grooves 4 will be formed accordingly; for example, 4-8 screw ribs 3 can be arranged, or preferably 6 screw ribs 3 can be arranged.

[0099] In addition, it can be further arranged that the ratio of the range occupied by each screw rib 3 to the range occupied by each feed slot 4 along the circumference of the screw is 0.5-2 times. That is, by adjusting the size of the screw rib 3 and the feed slot 4, the ratio between the gas injection time and the blocking time of the gas injection port 1 can be adjusted, thereby achieving the purpose of adjusting the gas injection effect.

[0100] In addition, for the shape of each screw fin 3, in theory, as long as it can meet the requirements of effective temporary blocking of the gas injection port 1 when it rotates and cooperates with the gas injection port 1 and can maintain a certain blocking time during the further rotation of the screw. When observed along the radial direction of the screw, the screw fin 3 is rectangular or parallelogram; of course, without loss of generality, the screw fin 3 can also be in other shapes that meet the above requirements.

[0101] In addition, under normal circumstances, the screw used in the extrusion foaming device is usually arranged in sections along the extrusion direction, and is generally provided with a feeding section 5, a shielding conveying section 6 and a screw fin mixing section 7 in sequence; at this time, the gas injection section 2 provided in the present invention can be preferably provided at the first screw fin position close to one end of the shielding conveying section 6 in the screw fin mixing section 7; that is, the gas injection section 2 in the present invention is actually a part of a section of the screw fin mixing section 7 that is closest to the shielding conveying section 6. The advantages of such a setting are: on the one hand, during the gas injection process, the shielding conveying section 6 can effectively prevent the injected foaming agent from flowing toward the feeding section 5; on the other hand, after the foaming agent is injected, the subsequent screw fin mixing section 7 can be used to mix the material melt with the foaming agent to a certain extent.

[0102] The screw mixing section 7 described in the present invention is mainly used to mix the material melt after the foaming agent is injected with the foaming agent to improve the mixing efficiency. In the present invention, the part of the screw mixing section 7 except the gas injection section 2 can be set to the same structure as the gas injection section 2 or a different structure, as long as the screw mixing section 7 can effectively mix the material melt and the foaming agent. Figure 5 As shown in the figure, the part of the screw flight mixing section 7 except the gas injection section 2 is set to the same structural form as the gas injection section 2, and all the screw flights inside the screw flight mixing section 7 as a whole can adopt the screw flight structure in the gas injection section 2; of course, in order to ensure the mixing effect in the screw flight mixing section 7, a certain distance can be left between adjacent screw flights along the axial direction of the screw.

[0103] In addition, refer to the attached Figure 1As shown in , the extrusion foaming device in the present invention includes a first extruder 8 and a gas injection device 9, and the gas injection device 9 is used to inject a foaming agent into the first extruder 8, wherein the foaming agent can be one or more of supercritical carbon dioxide, nitrogen, water, butane, and pentane. The gas injection device 9 usually uses a high-pressure gas injection pump for gas injection. The first extruder 8 includes a first barrel 10, and a first extrusion channel is provided in the first barrel 10. A first screw 12 is arranged in the first extrusion channel, and a first feed port 13, a first extrusion port 14 and a gas injection port 1 respectively connected to the first extrusion channel are arranged on the first barrel 10. The specific working process is as follows: the material enters the first extrusion channel through the first feed port 13, and then the material is pushed in the first extrusion channel by the rotation of the first screw 12 and heated to a material melt state by the heating section arranged outside the first barrel 10; then, the foaming agent is injected into the material melt in the first extrusion channel through the gas injection port 1 by the gas injection device 9, and then the foaming agent and the material melt are fully mixed and discharged from the first extrusion port 14.

[0104] The extrusion foaming device described in the present invention, wherein the first screw 12 is a screw for the extrusion foaming device described in the present invention, and at the same time, the first feed port 13 corresponds to the feed end on the first screw 12, the first extrusion port 14 corresponds to the discharge end of the first screw 12, and the gas injection port 1 corresponds to the gas injection section 2 on the first screw 12; the gas injection equipment 9 is connected to the gas injection port 1 through the gas injection pipeline 15; in this way, gas injection can be achieved through the cooperation of the gas injection section 2 on the first screw 12 and the gas injection port 1 set on the first barrel 10.

[0105] In addition, a one-way valve may be further provided on the gas injection pipeline 15; this can prevent the backflow effect during gas injection to a certain extent.

[0106] In addition, the number of gas injection ports 1 provided on the first barrel 10 can be one or more according to actual needs, and when multiple gas injection ports 1 are provided, the multiple gas injection ports 1 can be distributed at intervals along the circumference of the first screw 12 on the first barrel 10. Of course, the multiple gas injection ports 1 should correspond to the gas injection sections 2 on the first screw 12 respectively. Figure 2 and attached Figure 3 As shown in , two gas injection ports 1 are provided on the first barrel 10 , and the two gas injection ports 1 are further distributed symmetrically on the first barrel 10 relative to the axis of the first screw 12 .

[0107] In addition, the extrusion foaming device of the present invention may further include a second extruder 18, the second extruder 18 is connected in series with the first extruder 8, the first extrusion port 14 on the first extruder 8 is correspondingly connected to the feed port on the second extruder 18; a foaming die 26 is provided at the extrusion port on the second extruder 18. In this way, the present invention realizes connecting the two extruders in series, ensuring effective gas injection of the foaming agent and sufficient mixing between the foaming agent and the molten material before extrusion molding through the foaming die 26, thereby improving the operating stability of the extrusion foaming device.

[0108] More specifically, in order to improve the mixing effect of the second screw 21 on the material melt and the foaming agent, the present invention further provides that the second screw 21 includes a dispersion mixing section 36, and non-equidistant segmented dispersion thread sections 24 are sequentially arranged along the axial direction of the second screw 21 in the dispersion mixing section 36; the thread 25 located in the latter dispersion thread section 24 between two adjacent dispersion thread sections 24 starts between the two threads 25 in the former dispersion thread section 24; the specific structure can be referred to in the attached Figure 7 and attached Figure 8 As shown in ; the so-called non-equidistant segmentation means that the length distance of the dispersed thread segment 24 along the axial direction of the screw is not completely equal, and there is a certain variation. In this way, by setting the dispersed mixing section 36 structure, it can be ensured that the second screw 21 fully mixes the foaming agent and the material melt. In addition, in the present invention, a corresponding screw ridge mixing section 35 can be set on the second screw 21 along the extrusion direction, downstream of the dispersed mixing section 36. The function of the screw ridge mixing section 35 is also to further improve the full mixing effect of the foaming agent and the material melt, and the structure of the thread mixing section 35 can be set to the same structural form as the screw ridge mixing section 7 except for the gas injection section 2.

[0109] In addition, the first screw 12 and the second screw 21 in the present invention can also be set in association as follows: the screw diameter ratio of the first screw 12 and the second screw 21 is set to 1:1.25 to 1:3; at the same time, in the actual operation process, the speed range of the first screw 12 is set to 10 to 150 rpm, the speed range of the second screw 21 is set to 1 to 30 rpm, and the speed ratio of the first screw 12 to the second screw 21 is 1:5 to 1:50. Of course, the speeds of the first screw 12 and the second screw 21 and the speed ratio of the two can be appropriately adjusted according to the specific operating conditions. Through the above-mentioned association setting, the first extruder 8 can be operated at a relatively high screw speed to achieve good plasticization of the material and rapid and stable injection of the foaming agent, as well as preliminary mixing of the material melt and the foaming agent; while the second extruder 18 is operated at a relatively low speed to allow the material melt and the foaming agent to have more mixing time and reduce temperature and pressure fluctuations. More specifically, for the first screw 12, its length-to-diameter ratio can be further set to 1:25-1:40; and for the second screw 21, its length-to-diameter ratio can be set to 1:20-1:30.

[0110] In addition, the present invention can further provide a circulating cooling section on the first barrel 10, a coolant flow channel is provided in the circulating cooling section, and the circulating cooling section corresponds to the feeding section 5 on the first screw 12. The circulating cooling section can be provided on the first barrel 10 immediately downstream of the first feed port 13. By introducing a corresponding cooling medium, such as cooling water, into the coolant flow channel 7, the temperature of the material in the circulating cooling section can be controlled, so for materials containing volatile components, the volatilization of volatile components can be effectively prevented. Of course, whether to use the circulating cooling section to control the temperature of the material can be determined according to the specific material conditions.

[0111] The foaming die 26 described in the present invention can generally be various conventional foaming die structures such as a capillary die, a foaming flat slit die or a foaming annular die, depending on the different extrusion products required.

[0112] In addition, usually, in order to ensure that the material maintains a certain temperature condition in the foaming die 26, a corresponding temperature control device and sensor may be provided on the foaming die 26, and the specific conditions may be determined according to actual conditions.

[0113] The present invention will be further explained in detail with reference to the following examples. However, it should be understood by those skilled in the art that these examples are provided for illustrative purposes only and are not intended to limit the present invention.

[0114] Example

[0115] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present application and should not be considered as limiting the scope of the present application. The specific conditions not specified in the examples are carried out according to the conditions recommended by normal conditions or manufacturers. The reagents used or the instruments not specified by the manufacturer are all conventional products that can be obtained commercially. The application should not be construed as being limited to the specific examples described.

[0116] 1. Raw materials

[0117] Polyethylene terephthalate (PET): CB-602, Yuanfang Industrial (Shanghai) Co., Ltd.;

[0118] Polycarbonate (PC): Transparent fireproof V0, SABIC, density 1.19g / cm 3 ;

[0119] Carbon dioxide: purity> 99%, Chengdu Xuyuan Chemical Gas Co., Ltd.;

[0120] 2. Preparation method

[0121] (1) The following main raw material components are mixed by weight to form a mixed material:

[0122] Polyethylene terephthalate (PET) 84.4-98.4 parts,

[0123] Polycarbonate (PC) 1-15 parts,

[0124] Pyromellitic anhydride (PMDA) 0.6 parts,

[0125] The total weight of polyethylene terephthalate, polycarbonate and chain extender is 100 parts;

[0126] (2) adding the mixed material obtained in step (1) into a supercritical fluid extrusion foaming device composed of two extruders connected in series, wherein a gas injection port is provided on the barrel of the first extruder, the first extruder realizes continuous gas injection to ensure the smooth injection of CO2 foaming agent and prevent the CO2 foaming agent from escaping in the reverse direction, and the second extruder realizes uniform mixing of the materials, and extrusion foaming is performed through the capillary die of the second extruder to obtain a high-performance PET / PC composite foam material;

[0127] The temperature of the first extruder is 270-280°C, the temperature of the second extruder is 270-280°C, the temperature of the capillary die is 254-266°C, and the diameter of the capillary die hole is 2mm.

[0128] The screw speed of the first extruder is 20 r / min, and the screw speed of the second extruder is 1 to 15 r / min;

[0129] The continuous gas injection volume is 1-7 ml / min.

[0130] 3. Test methods

[0131] Foaming ratio calculation

[0132] For the PET / PC foam strips prepared by the extrusion foaming method, the density was determined by the water displacement method. First, a certain volume of water was measured in a measuring cylinder and the volume of water was recorded as V1. Then, the PET / PC foam strip with a mass of m was immersed in the water and the volume after the water surface rose was measured again and recorded as V2. The density of the foam strip can be calculated using formula (2-3).

[0133]

[0134] Scanning Electron Microscope (SEM) Testing

[0135] The morphology and pore structure of PET / PC foam products were observed using a scanning electron microscope (JSM-5900LV, Japan) at an accelerating voltage of 10 kV. Before observation, all samples were frozen in liquid nitrogen, and then the cross-section was obtained by cutting the middle of the sample with a double-sided blade, and then the surface was sprayed with gold. For SEM photo analysis, the number of cells, cell size, and cell distribution in the SEM photos were obtained by Nano Measure analysis. N (cell density) is calculated by formula (2-4):

[0136]

[0137] Where n is the number of cells in the SEM image, and A is the area of ​​the SEM image (cm 2 ), ρ0 is the density of the sample before foaming, and ρ is the density of the foam after foaming.

[0138] Embodiments 1 to 4

[0139] Examples 1 to 4 were prepared with reference to "2. Preparation method", and comparative experiments were conducted with the amount of polycarbonate added in the mixture as a variable, and finally high-performance PET / PC composite foam materials were prepared and tested as PET / PC foam strips.

[0140] Among them, in Example 1, the polycarbonate is 1 part in the mixture; in Example 2, the polycarbonate is 5 parts in the mixture; in Example 3, the polycarbonate is 10 parts in the mixture; and in Example 4, the polycarbonate is 15 parts in the mixture.

[0141] The test results are as follows Figures 11-12 shown.

[0142] Examples 5-6, Comparative Example 1

[0143] Examples 5 to 6 and Comparative Example 1 were prepared with reference to "2. Preparation method", and comparative experiments were conducted with the capillary die temperature as a variable, and finally high-performance PET / PC composite foam materials were prepared and tested as PET / PC foam strips.

[0144] Wherein, in Comparative Example 1, the capillary die temperature is 254°C; in Example 5, the capillary die temperature is 260°C; in Example 6, the capillary die temperature is 266°C.

[0145] The test results are as follows Figures 13-14 shown.

[0146] Examples 7-8, Comparative Example 2

[0147] Examples 7 to 8 and Comparative Example 2 were prepared with reference to "2. Preparation method", and comparative experiments were conducted with the gas injection amount of the continuous gas injection as a variable, and finally high-performance PET / PC composite foam materials were prepared and tested as PET / PC foam strips.

[0148] Among them, the continuous gas injection volume in Comparative Example 2 is 1 ml / min; the continuous gas injection volume in Example 7 is 4 ml / min; and the continuous gas injection volume in Example 8 is 7 ml / min.

[0149] The test results are as follows Figures 15-16 shown.

[0150] Examples 9 to 11, Comparative Example 3

[0151] Examples 9 to 11 and Comparative Example 3 were prepared with reference to “2. Preparation method”, and the screw speed of the second extruder was used as a variable for comparative experiments, and finally high-performance PET / PC composite foam materials were prepared and tested as PET / PC foam strips.

[0152] Among them, in Comparative Example 3, the screw speed of the second extruder is 1 r / min; in Example 9, the screw speed of the second extruder is 5 r / min; in Example 10, the screw speed of the second extruder is 10 r / min; in Example 11, the screw speed of the second extruder is 15 r / min.

[0153] The test results are as follows Figures 17-18 shown.

[0154] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

[0155] The references recorded in the background technology and invention content are as follows:

[0156] [1] Feng Yingjian, Hu Dongdong, Wei Shaolong, et al. Preparation of long-chain branched polyethylene terephthalate and study of its supercritical CO2 extrusion foaming properties[J]. China Plastics, 2023, 37(11): 1-9.

[0157] [2]Ge Y, Yao S, Xu M, et al. Improvement of poly(ethylene terephthalate)melt-foamability by long-chain branching with the combination of pyromelliticdianhydride and triglycidyl isocyanurate[J]. Industrial&Engineering ChemistryResearch, 2019, 58(9): 3666-3678.

[0158] [3]Kruse M,Wagner M H.Rheological and molecular characterization oflong-chain branched poly(ethylene terephthalate)[J].Rheologica Acta,2017,56:887-904.

[0159] [4] Champeau M, Thomassin JM, C,et al.In situ FTIR micro-spectroscopy to investigate polymeric fibers under supercritical carbondioxide:CO2 sorption and swelling measurements[J].The Journal ofSupercritical Fluids,2014,90:44-52.

[0160] [5]Chen Y,Yao S,Ling Y,et al.Microcellular PETs with high expansionratio produced by supercritical CO2 molding compression foaming process andtheir mechanical properties[J].Advanced Engineering Materials,2022,24(3):2101124.

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[0162] [7]Xia T,Xi Z,Yi X,et al.Melt foamability of poly(ethyleneterephthalate) / clay nanocomposites prepared by extrusion blending in thepresence of pyromellitic dianhydride[J].Industrial&Engineering ChemistryResearch,2015,54(27):6922-6931.

[0163] [8]Yan H,Yuan H,Gao F,et al.Modification of poly(ethyleneterephthalate)by combination of reactive extrusion and followed solid-statepolycondensation for melt foaming[J].Journal of Applied Polymer Science,2015,132(44).

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[0165]

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Claims

1. A method for preparing a high-performance PET / PC composite foam material based on supercritical CO2 extrusion foaming, characterized in that The main steps include: (1) The following main raw material components are mixed by weight to form a mixed material: 84.4 to 98.4 parts of polyethylene terephthalate, 1 to 15 parts of polycarbonate, Chain extender 0.6 parts, The total weight of polyethylene terephthalate, polycarbonate and chain extender is 100 parts; (2) adding the mixed material obtained in step (1) into a supercritical fluid extrusion foaming device composed of two extruders connected in series, wherein a gas injection port is provided on the barrel of the first extruder, and the first extruder realizes continuous gas injection to ensure the smooth injection of CO2 foaming agent and prevent the CO2 foaming agent from escaping in the reverse direction, and the second extruder realizes uniform mixing of the materials, and extrusion foaming is performed through the capillary die of the second extruder to obtain a high-performance PET / PC composite foam material.

2. The preparation method according to claim 1, characterized in that: The chain extender in step (1) is at least one of a polyepoxy chain extender, pentaerythritol, pyromellitic anhydride, glycerol triol, triglycidyl isocyanurate, glycidyl methacrylate, trimethylolpropane triacrylate, hexamethylene-1,6-diisocyanate, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, epoxidized cardanol, thermoplastic polyurethane elastomer, 4,4'-methylene terephthalate, a polyepoxy chain extender, 4,4'-diaminodiphenylmethane tetraglycidyl epoxy resin, tetrahydrophthalic acid diglycidyl ester, 4-vinylbenzyl glycidyl ether or a cyclic peroxide.

3. The preparation method according to claim 1, characterized in that: The temperature of the first extruder is 240-280°C, and the temperature of the second extruder is 250-280°C.

4. The preparation method according to claim 1, characterized in that: The screw speed of the first extruder is 20-100 r / min, and the screw speed of the second extruder is 5-20 r / min.

5. The preparation method according to claim 1, characterized in that: The polycarbonate in step (1) is 4 to 6 parts.

6. The preparation method according to claim 1, characterized in that: The diameter of the circular hole of the capillary die in step (2) is 2 mm, and the temperature of the capillary die is 260-266°C.

7. The preparation method according to claim 1, characterized in that: The continuous gas injection volume in step (2) is 3.8-7.2 ml / min.

8. The preparation method according to claim 1, characterized in that: In step (2), the screw speed of the second extruder is 5 to 10 r / min.

9. The preparation method according to claim 1, characterized in that: The chain extender in step (1) is pyromellitic anhydride.

10. The high-performance PET / PC composite foam material prepared by the method for preparing a high-performance PET / PC composite foam material based on supercritical CO2 extrusion foaming as claimed in claim 1.

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